Many areas of the food processing industry are concerned with sorting marketable or higher valued product from less desirable product. For example, the rice milling, nut processing and bean processing industries all sort bulk product to weed out lower quality or aesthetically unpleasing product.
In the rice milling industry, for example, whole grain yield is highly valued. A broken grain is worth half or less in the marketplace compared to a whole grain. Also, a small difference in the amount of broken grains level in the milled rice will significantly lower its quality grade. As such, broken grains are removed from milled rice and sold off at a lower price.
The rice `milling` industry consists of two general types of rice mills: white rice mills and parboiled rice mills. In a white rice mill the rough rice is dehulled and milled, along with numerous mechanical cleaning and defect separation operations. In a parboiled rice mill, the rough rice is steeped in hot water, steamed, dried, dehulled and milled, along with numerous mechanical cleaning and defect removal operations. Parboiling has several advantages for improving the rice's cooking quality and milling yield.
For a white rice miller, brokens in milled rice are in part caused by imperfect grain structure. These are immature grains, chalky grains and internally cracked grains in rough rice. Immature grains are underdeveloped, are generally thin and break easily. Chalky grains have milk-white or opaque centers and are sometimes called white bellies. Chalkiness is caused by the presence of air or due to less dense packing of starch in the endosperm. It is soft and also breaks easily. Cracked kernels are caused by either over drying prior to harvest, uncontrolled moisture adsorption or desorption, mechanical harvest damage, or by some other post harvest damage. Rapid or uncontrolled moisture change causes mechanical stress in the rice kernel. If the stress exceeds the tensile strength of the kernel, a crack or check is the result. For parboiled rice millers, neither chalk nor cracked grains cause breakage as they are almost completely healed during the hydro-thermic processing. Thus, parboiled rice millers have a whole kernel yield advantage over white rice millers. This disadvantage could be eliminated, if the white rice millers could obtain crack and chalk free rice for milling.
In another example of the tree and ground nut processing industry, the value of the nuts are significantly influenced by the presence of foreign material and defective nuts. The foreign material and defects can include but not be limited to unblanched nuts, discolored nuts, mold, immature nuts, nut grass seeds, glass, stones, metal, nut skins, nut shell, stems, and corn.
In the nut industry, nuts are removed from the shell by means of mechanical crackers, blown and separated from the shell material and classified by density size. This process does not efficiently or completely remove undesirable material from the nut meat. Defects and foreign material still remain with the good product and additional efforts must be employed to further reduce the level of the undesirable to an acceptable level. The additional capital equipment and personnel required to produce this highly segregated material result in a high cost to the user. This puts consumer nut product producers at a price disadvantage due to the high processing costs required for the premium quality nuts. To offset a portion to the reprocessing and separation costs, nut processors have employed electronic sorters to reduce the quantity of good product in the waste material stream to improve overall yield. Further, these sorters are used to remove foreign materials to maintain an acceptable quality level. Therefore a producer is faced with balancing the cost of raw material with varied quality attributes and the cost (or yield) of the resulting finished product. A distinct advantage to a producer can be realized if the efficiency and capital cost of the sorting equipment can be technologically optimized.
The following disclosures are related to the sorting process used in the present invention. Massen, et al., U.S. Pat. No. 5,524,746, discloses an apparatus for sorting bulk rice using an optical monitor to detect grains of different color or luminosity or grains of different size or shape that travel on a conveyor belt. When the optical monitor detects an imperfect rice grain, a jet of air from a nozzle removes the grain from the conveyor belt. Satake, et al., U.S. Pat. No. 5,245,188, discloses an apparatus for evaluating the grade of rice grains using grooved chutes in which the individual grains fall through past a light source. Detectors measure both the reflected and transmitted light from each grain and determine if the grain is complete, scratched or discolored. Inferior grains are sucked from the grooved chutes and removed through a different outlet. Satake, U.S. Pat. No. 4,806,764, discloses an apparatus for evaluating the quality of rice grains using an infrared spectrometer with a band-pass filter and detectors for measuring reflected light to measure the content percentages of pre-selected constituents, such as protein, amylose, amylopectin, and moisture. From the various content percentages, quality evaluation values are determined. Satake, U.S. Pat. No. 4,752,689, is related to the previous patent except that it prints or displays the actual percentage contents of constituents. Gillespie, et al., U.S. Pat. No. 4,666,045, discloses a pit detection apparatus and method for fruit sorting using a sweeping transmission scanning beam with sensors and a sizing beam with sensors. Pits are detected from analyzing the amount of light transmitted through the fruit at various points in the fruit. Fruit with pits are then removed by an ejector valve. Satake, U.S. Pat. No. 4,572,666, discloses an apparatus for detecting cracked rice grains in hulled or unhulled grains using a chute or conveyor belt, a light source, and two light detectors. Cracked grains are determined by comparing the amount of light transmitted through leading half part of an inspected grain to its trailing half part. Based on the grain's position, less light will be transmitted through one-half of a cracked grain in comparison to the other half. Pilesi, et al., U.S. Pat. No. 4,196,811, sorts buttons by measuring the amount of light transmitted through each button as it travels down a chute. Murata, U.S. Pat. No. 3,871,774, detects cracks in unhulled grains by irradiating the grain with a laser and measuring the light transmitted through the grain which is conveyed through the laser beam. The amount of light transmitted through the grain decreases when a crack is scanned. The patent does not disclose a method to sort the grains, a laser line, a means to separate grains for detection, a grain stabilizing means, or any features to make the invention commercially efficient. Fraenkel, U.S. Pat. No. 3,197,647, sorts white from red rice by measuring the light transmitted through each grain. Twamley, U.S. Pat. No. 1,031,669, tests the maturity of corn kernels by transmitting light through the kernels. Brizgis, et al., U.S. Pat. No. 4,713,781, analyzes damaged grain by illuminating a grain with long wave, ultraviolet radiation, causing the exposed starch of the damaged section to fluoresce. The amount of fluoresce determines the amount of damage to the grain.
Generally, sorting equipment for product falls into two basic categories: gravity chute type and belt type. In the gravity chute type the product stream is divided and fed into multiple, parallel chutes designed to place the product into a single row of material, sliding down a "v" channel chute. The purpose of this is to present the product in front of a detector, one individual piece at a time. The negative result of this method is that the product is not under any positive control, once it begins its descent down the chute. This results in varying velocities and spacing at the chute discharge. These variables act together to allow the individual product to wobble down the chute and not be perfectly aligned with the detector. This alignment is critical to the capability of the sorter to detect and accurately reject unacceptable material. The light source used to illuminate the product as it falls past the detectors can be incandescent or florescent. The type of defect that can be seen is determined by the wavelength of the light source and/or suitable filtering over the detector.
In the belt type sorter, the product is fed onto a high-speed (approximately 150 m/minute) belt in a manner to distribute the product such that each individual piece is not touching. The product is illuminated and detected at the end of the belt while it is in free fall. Undesirable material is rejected at this point. Illumination can be with florescent or laser light sources. Specific wavelengths are also obtained with the use of filtering and/or specific wavelength sources. The method of illumination with a laser is by use of a laser produced beam of light which is reflected off a multi-faceted rotating mirror, creating a line of light across the belt. Since the line is really a spot of light moving across the belt, it does not completely illuminate the product as it passes by it. This results in a maximum potential accuracy that is directly proportional to the number of times that each individual product is scanned.
In either case, the use of lasers provides a much higher intensity of light to illuminate the nuts making the sensitivity of the detection system less critical. Lasers are coherent light sources. This allows selection of specific wavelengths of light to be used, tuning the unit to specific undesirable materials. It can be seen in the above descriptions that an improvement in accuracy can be realized if the presentation of the product to the detector is made repeatable and the laser is made to scan more frequently or employ use of a continuous line of laser generated light.
With the conventional apparatus or methods disclosed above, it is not possible to sort many products in a commercially efficient manner for use. For commercial purposes, the evaluation of product must be done quickly with minimum error. In the previously disclosed art, an individual product travelling at a high velocity may not be properly stabilized when it is analyzed because air resistance and other factors may oppose the natural product orientation. If the product is wobbling, a structural defect may not be detected. The prior art also does not disclose adequate methods for separating product prior to analysis using a chute. Additionally, the lasers used to analyze objects in the previously disclosed art are typically focused to the smallest spot size possible and do not illuminate some defects that are not precisely positioned. Also, the photo detection systems used do not provide a strong signal for better resolution of the signal. With a commercially efficient sorting invention, product could be separated into two fractions: selected and unselected product. Then, for example, white rice millers could process the internally whole unhulled grains for a higher yield for those who would pay a premium price for the internally whole unhulled grain. The internally defective unhulled grains--which would have resulted in broken rice for the white rice millers--can be used by parboilers for processing.